Cryopumping may be defined as the removal of gas from a chamber by solidifying the gas molecules therein onto a cold surface to produce a very high vacuum within the chamber. In large installations, such as space simulation chambers wherein the present apparatus is designed for use, the pumping speeds required are large. These speeds may be achieved by placing the cryopump inside the chamber. The cryopump surfaces are cooled to ultra low temperatures and are shielded in order to reduce heat absorption by these surfaces from their surroundings. Since heat transfer to these surfaces is effected almost totally by radiation, the cryopump surfaces are generally surrounded by suitably configured radiation shields maintained at substantially liquid nitrogen temperatures. Unfortunately however, shielding reduces pumping speed by requiring the molecules of the gas to be evacuated to be pumped along a more circuitous path prior to solidification.
Shielding array configurations of prior art cryopumping devices are many and varied. None however are believed capable of cryopumping equally on both sides while yet providing high pumping speeds for producing ultra high vacuums in a large chamber, such as a space simulation chamber, for example, and additionally providing cooperating structure permitting free and safe movement of various components of the device due to thermal expansion and contraction, thus obviating the need for periodic alignment, adjustment, and repair.
The present invention employs Z-shaped shields optically blinding cryogenic panel members, and includes structure cooperating therewith for passage of cryogenic and refrigerant fluids. The "floating" construction of the present cryopump assembly permits the necessary movement of certain components due to thermal contraction and expansion without reducing the efficiency and pumping speed of the apparatus.